Portions of this disclosure are described in terms of, e.g., encoded signals for digital designs, product packaging (sometimes just referred to herein as “packaging” or “package”), hang tags, labels and other objects. These encoding techniques can be used, e.g., to alter or transform how colored inks are printed on various physical substrates. The alterations or transformations preferably result in a printed design carrying machine readable indicia on a surface of a physical object.
Various forms of signal encoding (or “embedding”) include, e.g., “steganographic encoding” and “digital watermarking.” Digital watermarking is a process for transforming physical or electronic media to embed a machine-readable code (or “auxiliary data”) into the media. In some cases the media is transformed such that the embedded code is “obscured” or “generally imperceptible” relative to an overt symbology (e.g., 1D or 2D barcode), yet may be detected through an automated detection process. Obscured and generally imperceptible in this context means that the luminance/chrominance variations in the artwork due to the digital watermarking are not noticeable to a human viewer inspecting the package from a usual distance (e.g., 20 inches) under normal retail lighting (e.g., 50-85 foot candles), who has not previously been alerted to the existence of the digital watermarking.
Digital watermarking is often applied to electronic or physical objects such as printed objects, images, audio signals, and video signals. However, it may also be applied to other types of objects, including, e.g., product packaging, electronics such as circuit boards and CPUs, stickers, logos, product hang tags, line-art, software, multi-dimensional graphics models, and surface textures of such objects.
In this document we use the terms “digital watermark” and “watermark” (and various forms thereof) interchangeably.
Auxiliary data embedding systems typically include two components: an encoder (or embedder) that embeds the auxiliary signal in a host image or object, and a decoder (or detector) that detects and reads the embedded auxiliary signal from the host image or object. The encoder may embed the auxiliary signal by altering or transforming a host image or object to carry the auxiliary data. The detection component analyzes a suspect image, object or signal to detect whether an auxiliary signal is present, and if so, extracts or reads information carried in it.
Several particular digital watermarking and auxiliary data embedding and detection techniques have been developed. The reader is presumed to be familiar with the literature in this field. Particular techniques for embedding and detecting imperceptible digital watermarks are detailed in the assignee's patent documents including US Published Patent Application Nos. 20150156369 and 20160217547; U.S. Pat. Nos. 9,635,378 and 9,819,950; International Application No. PCT/US2015/44904, filed Aug. 12, 2015 (published as WO 2016025631 A1) and U.S. Pat. Nos. 7,054,461, 7,286,685, and 9,129,277. Related technology is detailed in Assignee's U.S. Pat. No. 9,754,341. Each of the patent documents mentioned in this paragraph are hereby incorporated herein by reference in its entirety, including all drawings and any appendices.
We have recently developed a technology to handle encoding dark colored inks and/or multi-colored ink designs (e.g., Cyan (C) Magenta (M) Yellow (Y) or CMYBlack(K) printed designs) such as are often printed on packages, label, tags, and/or containers. A dark colored ink/design is one that comprises a spectral reflectance less than or equal to 20%. This technology is particularly useful in printing environments lacking tight color to color registration (e.g., able to hold a 1/12″ color to color registration).
One solution for encoding dark color inks includes overprinting a “Digimarc Dark ink” or “Digimarc Dark resin.” The overprinted Digimarc Dark ink/resin comprises a carrier for an encoded signal. Overprinting here refers to a process of printing one color on top of another. One example of a Digiamrc Dark ink includes an ink mixture including a spectral reflectivity greater than a dark ink in the spectral region of 620-700 nm. The dark ink comprises a spectral reflectivity of less than or equal to 20% at or around 660 nm. To minimize visibility, the overprinting ink mixture includes a spectral reflectivity less than the overprinted dark ink in the green spectral region (about 495-570 nm).
One aspect of the disclosure is a printed object. The object includes: a substrate comprising a first area; a first ink printed within the first area, the first ink comprising a spectral reflectivity of less than or equal to 20% at or around 660 nm; a ink mixture printed over the first ink at a first plurality of spatial locations within the first area, the ink mixture printed such that the first area comprises a second plurality of spatial locations without the ink mixture, the ink mixture comprising opaque white ink or opaque white resin and a first selected colorant, wherein the ink mixture comprises a spectral reflectivity greater than the first ink. The first plurality of spatial locations is arranged in a pattern conveying an encoded signal, and the first ink and the ink mixture comprise a spectral reflectivity difference at or around 660 nm in a difference range of 8%-30%. The ink mixture comprises a spectral reflectivity less than the first ink in the spectral region of 495 nm-570 nm.
The ink mixture may include multiple colorants of which in combination meet the spectral relationships discussed above. In one example, the ink mixture is colored by Lithol Rubine pigment and by Carbazole Violet pigment. In a further example, the ink mixture comprises by weight or volume 30%-42% Lithol Rubine, 8%-22% Carbazole Violet and 44%-56% Opaque White. In a specific example, the ink mixture comprises by weight or volume 36% Lithol Rubine, 14% Carbazole Violet and 50% Opaque White.
In another example, the ink mixture is colored solely by Lithol Rubine. In such example, the volume or weight ratio for the ink mixture may include 24%-32% Lithol Rubine and 68%-76% opaque white. Still further, the volume or weight ratio for the ink mixture may include 78% opaque white and 22% Lithol Rubine.
An example encoded signal includes a sparse mark and carries a plural bit identifier payload.
Another aspect of the disclosure is an image processing method. The method includes: obtaining optically captured imagery representing a printed object, the imagery captured by a scanner have a peak illumination at or around 660 nm. The printed object comprises: a substrate or background comprising a first area including a first colored ink printed therein, the first colored ink comprising a spectral reflectivity of less than or equal to 20% at or around 660 nm, the first area further comprising an ink mixture printed at a first plurality of spatial locations within the first area and over the first ink, the ink mixture printed such that the first area comprises a second plurality of spatial locations without the ink mixture, the ink mixture comprising opaque white, first colorant and second colorant, in which the first plurality of spatial locations is arranged in a pattern conveying an encoded signal carrying a plural-bit payload, and in which a reflectivity difference at or around 660 nm between the first ink and the overprinted ink mixture comprises a difference in the range of 8%-30%. The method further includes processing the captured imagery to decode the plural-bit payload from the encoded signal, and outputting the plural-bit payload.
In one example, the ink mixture comprises a spectral reflectivity less than the first ink in the spectral region of 495 nm-570 nm.
Further aspects, features, combinations and advantages will become even more apparent with reference to the following detailed description, claims and accompanying drawings.